“For days in 2012, we watched those white and gray clouds of smoke and wondered if we would lose our home, and now we dread seeing the dark rain clouds come up. Our town is still under threat because of floods that came after the fire,” says a resident of Manitou Springs, CO.
Erosion control specialists are well aware of the threat of flooding that follow wildfires. Once the land is scorched and stripped of vegetation, runoff rates often increase exponentially. In addition, debris and sediment flows cause complications downstream. The cost of a fire can be extremely high, both in emotions and in dollars. However, often the monetary costs of the flooding that follows a fire can be even greater.
As much of the western United States is still experiencing severe drought and wildfires have become a usual summer phenomenon, more and more communities will face the devastation of fire, followed by floods bringing heavy sediment damages.
Mitigation BMPs are essential to put into place after the fire, but assessing what is needed, getting funding, and carrying out the work takes time, meaning that flooding may have already occurred. Once the measures are in place, vegetation establishment requires even more time.
In many cases, such as the events in Colorado covered in this article, there is no buffer zone between canyons where the fires occur and the communities. Government agencies from federal to local must be prepared to fight the fire and then deal with the succeeding runoff challenges.
First the Fire
The Waldo Canyon wildfire began on June 23, 2012, in the mountains and canyons, including Williams, west of Colorado Springs, CO. It burned for 18 days and destroyed 18,247 acres. Two people died, and 347 homes in the Mountain Shadows neighborhood were destroyed after the fire jumped ridges into the city of Colorado Springs.
Then the Flooding
The flooding problems for communities west of Colorado Springs began less than a month after the fire was contained. On July 30, 2012, about 1.5 inches of rain fell over 80% of the burn scar and caused flooding that destroyed a water supply pipeline and closed Highway 24 due to a mudslide. Ute Pass Elementary School was damaged from the flooding and debris.
During 2013, flood runoff from the burn scars ravaged Ute Pass communities several times. On August 9, 2013, the worst flooding in decades hit Manitou Springs, a town just west of Colorado Springs at the foot of Pikes Peak. One man died and numerous homes and businesses were destroyed. Highway 24 was closed off and on for days because of flooding and the risk of mud slides.
In September 2013, between 5 and 8 inches of rain fell over five days. Flash flooding occurred down Ute Pass along Highway 24 and in all four watersheds that had been affected by the fire. The flooding led the President to declare the site a disaster area, allowing for Federal Emergency Management Agency (FEMA) money to be granted.
As a precaution, the Colorado Department of Transportation has started closing Highway 24 when the National Weather Service issues a flash flood warning. The highway is the main route through Ute Pass into mountain recreational areas, so the closures have a big impact on many communities and businesses. People who live in the communities in the Ute Pass area and work in Colorado Springs are inconvenienced when they must sit on the highway waiting for it to reopen. More than 26,000 vehicles travel the highway each day. The “better safe than sorry” approach is wise, but it carries a big cost. CDOT is hoping that as flood control measures show effectiveness, the closures can be reduced.
Mitigation Measures
A Burned Area Emergency Response (BAER) team assessed the damage done by the Waldo Canyon Fire. The team determined that 14,422 acres of the burned land was on National Forest System lands, 147 on Department of Defense land, and 3,678 are on non-forest lands.
Emergency stabilization work began as soon as the initial assessment was made. Bradco Environmental of Redlands, CA, was contracted to use helicopters to drop agricultural straw and shredded wood mulch on 3,038 acres of National Forest System land. More than 8,000 tons of the materials was applied. Flash flood warning signs were installed, severely burned areas were closed to the public, and some trees that presented immediate hazards were removed. Log erosion barriers and wattles were placed across slopes by hand crews. These mitigation efforts reduced the risk of flooding, landslides, and debris flows, but treatments on private and other land still needed to be done to increase the safety level.
Remote rain gauges and cameras have been installed in the upper canyons by the US Forest Service. Viewers can see the precipitation amounts and also the amount of water running through the streambeds, giving some notice of how heavy the downstream flow might be.
In April 2013, “The Waldo Canyon Fire Master Plan for Watershed Restoration and Sediment Reduction” was released. The report was coordinated with numerous groups and agencies, including the Pike National Forest, the Natural Resources Conservation Service, the Colorado Water Conservation Board, city and county agencies, and the Coalition for the Upper South Platte. The assessment and plan were done by Wildland Hydrology of Fort Collins, CO; Blue Mountain Consultants in Berthoud, CO; and the US Forest Service using the WARSSS (Watershed Assessment of River Stability and Sediment Supply) methodology. This method allows for a quick but thorough assessment of land and channel stability and the possible impacts downstream.
The Waldo Canyon fire burned over four main watersheds: Camp Creek, Monument Creek, Douglas Creek, and Fountain Creek. The watersheds were divided into subwatersheds for more detailed analysis. Twenty-four were assessed as low risk, with stable channels or low burn severity, so they were not further analyzed. Eighty-nine subwatersheds were designated as high risk and were studied in more detail. The slopes are steep and have only limited access, which also restricts mitigation measures that can be applied.
Part of the data used for the WARSSS report included the BAER team’s study of runoff response. The combined studies showed that the 89 high-risk subwatersheds cover 24,248 acres, with 71% of that area burned. The severity of the burn: 32% low intensity, 34% moderate intensity, and 5% severe intensity. The sediment load was estimated to be 51,470 tons per year with 61% from streambed erosion, 35% from surface erosion, and 4% from road sections. The soil is decomposed granite, so it erodes easily. Most streams already had a heavy sedimentation rate before the fire.
The Waldo Canyon Regional Recovery Group was formed, including El Paso County, the cities of Colorado Springs and Manitou Springs, the utilities, the Colorado Department of Transportation, the US Forest Service, and other organizations. The group “determined the top 10 areas in which to place mitigation structures on and alongside the burn scar to protect lives and property,” according to Gordon Brenner, MPA, fire recovery coordinator for the Office of Emergency Management for Colorado Springs. Mitigation work accomplished by the group in 2013 added up to more than $30 million, and much more remains to be done.
The area receives the majority of its annual rainfall as brief but heavy downpours, adding to the chance for heavy stream flow and sediment load. Some of the streams are prone to aggradation, while others face degradation. The effects of the stream flow peak are estimated to be long term, from 50 to 75 years, before complete restoration.
The restoration plan divided the sediment supply sources into hill slopes, roads and trails, and channels and provided a framework for sediment control projects. Flow charts were developed to show the type of work to be accomplished, whether it would be by equipment or by hand, and the purpose, such as for surface protection, flow dispersion, or grade control.
The seed mix provided was developed in conjunction with the US Forest Service and Jonathan Bruno, operations director of the Coalition for the Upper South Platte, headquartered in Lake George, CO. The special mix was prepared just for the Waldo Canyon burn scar by Western Native Seed of Coaldale, CO. Revegetation also includes nursery plants of oats and trachycaulus. These plants quickly establish themselves and provide protection for the native seeds. The natives grow in more slowly, and the nursery plants fade away after a few years. The native seed used for Waldo Canyon included western wheatgrass, blue grama, junegrass, bottlebrush squirrel tail, and little bluestem.
One Subwatershed
John Chavez, stormwater quality coordinator for El Paso County, took the author on a tour of one subwatershed. It drains into a small town, Cascade, that is stretched out along Highway 24. The tiny creek that flows down the mountain has no name, but flooding and heavy sediment deposition had occurred after the storms of 2013, especially the multiday event in September.
The subwatershed was divided into upper, middle, and lower channels with mitigation measures applied to each level. The upper channel has a dirt road twisting through, so rain bars were made to force the water flow in the desired direction. Log sills were installed across the channel using the available burned materials, and 36- to 48-inch rocks were placed to slow the flow. Sedimentation basins were built and lined with TenCate Mirafi geosynthetic fabric. Erosion control blankets were applied over topsoil and a seed mix that included quick-growing annuals and native seeds.
Because of the cost, these sediment basins will not be maintained, but they have already proved their worth by retaining substantial amounts of sediment. As Brenner says, “The basins captured sediment and created alluvial fans on, above, and below the basins.”
One of the basins near the top of the subwatershed was about one-third full from the rains of 2014. The recent rains have brought up the annual seed mix and native varieties are growing in, forming a good vegetation system.
The middle channel adds a riprap installation in the streambed, along with rain bars and grade control measures. At the bottom of the middle channel is a cleanable catch basin. Before mitigation work was done in this subwatershed, the area of the catch basin was covered with up to 6 feet of sediment after heavy rains. Homes in the area were flooded, and roads washed out. After installation of the upstream mitigation, the recent rains filled the catch basin about half full and no home flooding occurred. Continuing work will further reduce the risk. Chavez notes that for these early years, the catch basin will likely have to be cleaned out after every other storm of significant rainfall and sediment loading.
The lower channel is very narrow and runs right into the town. Sheet piling was installed along the streambed to prevent erosion of the channel banks. Trapezoidal (TRAP) and Rapid Installation Barrier Systems (RIBS) were installed near homes and public areas to provide strength against floodwaters. Sandbags were available to residents for protection of their homes.
Some Success
Chavez was pleased to see the measures working after rain events of the week of July 15-19, 2014. Afternoon thunderstorms dumped 0.5 to 0.75 inch on July 15 and 16 and about 1.3 inches on July 19. The sediment control measures had performed splendidly when viewed on July 22.
Viewing the work done on this one subwatershed and all that remains to be accomplished demonstrates the gigantic scope of the challenge. The subwatersheds with the highest potential for loss of life or property are being mitigated, but others will have to wait or have no mitigation at all.
On Target for Flooding
The town of Manitou Springs is in the target area for flooding after the Waldo Canyon fire. Both Waldo Canyon and Williams Canyon drain into creeks that run through the town. The town is a highly prized tourist destination, but the fire in 2012 and flooding in 2013 caused a decrease in tourist traffic. Businesses that were already struggling from loss of tourists were slammed by flooding in July 2012 and in July, August, and September 2013. Some shop owners decided to move their businesses because of the high cost of cleanup and insurance.
In August 2013, a 4-foot wall of water, debris, and mud ravaged the town. Six houses were destroyed and 11 severely damaged, and one man died.
Roger Miller, flood recovery manager for Manitou Springs, says approximately 10,000 cubic yards of sediment were removed from Fountain Creek, which runs through the town. The sediment came from both Waldo and Williams canyons. While the Waldo Canyon sediment is decomposed granite like most of the rest of the area, that from Williams Canyon is limestone cobble. It shows up as lighter flakes in the sediment deposited in the creek.
After a flood caused damage in the Williams Canyon drainage in 1999, gabions were installed along the streambanks. They were failing under the debris and sediment load after the wildfires. The decision was made to replace them with a soil nail wall and cast concrete at a cost of $5.5 million. A 7-foot by 7-foot culvert replaced smaller ones under Canon Avenue, one of the main streets in town.
Other sediment control measures are in place in Williams Canyon, leading into Manitou Springs. They include sediment basins, log and wattle barriers, and hill slope stabilization.
Money for the Waldo Canyon restoration and mitigation work came from a variety of sources, including the Natural Resources Conservation Service (NRCS), FEMA, and local governments. In addition, more than 6,500 volunteers dedicated 47,700 hours performing tasks such as hand work to stabilize slopes and planting seeds and willow plugs. A September 2013 update report on the Waldo Canyon restoration estimated that detention basins had captured more than 14,000 tons of sediment and debris, much of which would have ended up in Manitou Springs without the mitigation.
Miller says one thing that he has learned is that the city needs to work to obtain funding sources for long-term maintenance, not just for the initial years of mitigation.
High Park Fire
A fire in northern Colorado was burning even before the one that started in Waldo Canyon. Known as the High Park fire, it also was much larger in size, burning more than 87,200 acres from June 9 to July 1, 2012. The fire was started by lightning in the forest land northwest of Fort Collins and was 100% contained after 21 days. Losses included one life and 259 homes, making it the third-largest fire in Colorado history. The Waldo Canyon fire surpassed that number of homes lost in the following weeks, and in 2013, the Black Forest fire burned more than 500 to become the largest ever in terms of damage in Colorado.
The BAER team consisted of specialists from the NRCS, the US Forest Service, Larimer County, and the Colorado Department of Transportation. The team estimated that $24 million would be needed for emergency stabilization treatments, half of which might come from the Emergency Watershed Protection program.
A survey of the area found that about 21% was burned at high severity, 52% at moderate severity, and 27% at low severity. Several patches of unburned area lie inside the burned portions.
Emergency stabilization measures included aerial mulching for 5,597 acres on National Forest Systems lands, road repairs, closures of sections that had previously been open to the public, noxious weed detection and treatment, and trail stabilization. Private lands would need similar mitigation. The mulching was confined to areas with high to moderate soil burn severity and slopes between 20% and 60%.
Flooding and Sediment Protection
One critical target for protection is the Poudre River, a source of drinking water for more than 300,000 people. Municipal water supplies for three areas-Fort Collins, Greeley, and the Tri-Districts-are severely impacted. Reservoirs are expected to suffer from sedimentation and debris flows, and some irrigation systems were also damaged.
In all, nine watersheds were impacted by the fire. Erosion potential changed from 1 ton per acre pre-fire to 23 tons per acre post-fire. Soils include extremely cobbly loamy sand, very gravelly coarse sandy loam, and sandy loam, all with between 5% and 35% rock content. A variety of vegetation grew in the burned areas, including grass and low-growing brush, oak, and aspen mix, and ponderosa and lodgepole pine.
The two small communities of Poudre Park and Bellvue are each located at a confluence of affected watersheds. Even a small rain a month after the start of the fire caused flooding. A variety of roads are at risk for flooding, including Colorado State Highway 14, which is the main route into recreational areas.
A report written by the Colorado State Office of the NRCS and published in October 2012 stated that a 10-year rain event in the post-fire areas could cause 50- or 100-year floods, leading to a 40% chance of having such a flood in the five years following the fire.
Hydrophobicity has been shown to be higher in soils with increased sand content. The effect weakens after a few months, but in the ponderosa and lodgepole pine forest of Colorado, the result can last up to two years.
Modeling for the hydrologic analysis of the High Park fire was performed using HEC-HMS, version 3.5. Using data from NRCS and the US Geological Survey, including soil burn severity, the model predicted that discharge rates would increase substantially on all streams. For example, with a 10-year rain event, Boyd Gulch would show a discharge of about 100 cubic feet per second (cfs) before the fire and 420 cfs post-fire. Hill Gulch showed the largest increase-from 300 to 1,100 cfs. These impacts will persist for at least five years, and mitigation measures must take that into account.
Mitigation BMPs
Mitigation measures continued after the initial aerial drop of seed and mulch. Mark Peterson, P.E., engineer for Larimer County, says the county considered many BMPs to reduce flooding potential. Sedimentation basins were considered but discarded as impractical for two reasons. First, there was not enough area and volume available compared with the expected sediment generated. Second, it is not possible to construct the basins without a supportive landowner, and most of the affected areas were on private property.
Some sandbagging around homes and other structures was accomplished. Only a small concentration of buildings was at risk. More attention needed to be given to roads that twist through the area and that were at risk of failure due to heavy sediment and debris runoff.
“We decided to allocate about $2 million in county resources to replace seven undersized culvert crossings in Rist Canyon that were at risk of plugging or being overtopped, eroding, and failing,” says Peterson. Woody debris along the canyon was removed and more rainfall and stream gauge monitoring stations were installed to provide real-time flood warning. The Colorado Department of Transportation also replaced culverts along State Highway 14 to handle increased water and sediment flow.
Two residential subdivisions were experiencing heavier water and sediment flows, so channels were improved and will be monitored to see if further treatment is needed.
Skin Gulch had suffered several flood events, with heavy sediment coming from the burn scar. The area was mitigated with extensive riprap bank protection, giving stabilization to the county road. The city of Fort Collins completed a channel stabilization project to protect a major water supply pipeline.
Challenges and Successes
The cities of Fort Collins and Greeley cooperated in an aerial seeding and straw mulching operation in the Poudre River and Big Thompson River watersheds in fall 2012, just a couple of months after the High Park fire. The success rate varied. In some areas, the straw was moved by intense rainstorms or high winds. In summer 2013, they decided to use woodshred mulch instead. During extensive rainfall over several days in September 2013 the wood mulch held up well.
In several areas, burned timber was used as log barriers, and more will be used as the burned trees begin to fall over the next three to five years.
Thousands of volunteers from Wildland Restoration Volunteers have offered their time for seeding, planting seedlings, and other projects over the burn area. The Community Tree Recovery Campaign offered more than 4,000 free seedlings to landowners in 2013, and the supply ran out before all requests could be filled.
In 2014, donations from Northrop Grumman Corporation and FedEx allowed the campaign to increase the supply of seedlings to 10,000. Eight varieties of trees were available, matching the natural forest.
As in the Waldo Canyon burn scar, the area of the High Park fire faced heavy rainstorms in the fall of 2013. Large amounts of sediment were deposited in the Poudre River and in tributaries of the Big Thompson River. Rist Canyon flooded and the culverts were overtopped, but the road held. Peterson says, “We believe that we definitely would have seen significant road failures if we had not decided to construct new culverts in anticipation of the post-fire impacts.”
Challenges
Specialists, working with government agencies or for private companies, faced a variety of challenges in these post-fire environments. Many of these lessons learned are applicable to other parts of the country that might confront the same issues. Other Western states have experienced multiple fires and have worked out procedures to start the mitigation measures as soon as possible.
- Topography and climate-Colorado has steep canyons, multiple watersheds, heavily forested terrain, and a dry climate that receives rain in brief but intense events. These factors combine to make Colorado a beautiful state, but one that faces the possibility of catastrophic fires, followed by devastating floods.
- Damage over different ownership areas-Fires affect National Forest System lands, resources owned by other government agencies (such as states, counties, and cities), and private land. This combination of ownership leads to a conglomeration of challenges when the money from grants is being used. For example, NRCS money cannot be used on roads. Careful accounting must be taken to ensure that the right money goes to the right part of the project.
- Lack of buffer between canyons and communities-Because the canyons and streams drain directly into the towns, the potential for sediment deposition and flooding increases dramatically.
- The cycle that brings fires at the dry season, just before the heavy rains of the monsoon season-In Colorado, June is typically warm and dry; in July, heavy rains can fall from moisture that sweeps up from the south. Little time for installation of mitigation measures can be expected after a fire.
- Timing-The length of time to assess restoration requirements, receive money and supplies, and accomplish the work is often much longer than the time between fire and flood.
Colorado has experienced the devastation of fire and flood but has learned valuable lessons. Governments have developed plans so that mitigation can begin as soon as possible. In addition, volunteer organizations such as the Coalition for the Upper South Platte are an invaluable resource for hours of in-kind work that allow the projects to proceed with the available money.
In the summer of 2014, fires raged across Washington, Oregon, Utah, and California. Those areas will be facing many of the same and probably some different challenges. Seeing what has worked or not worked in other places reduces the learning curve, and we can all benefit from the experience of others in the post-fire environment.
